The present invention relates to a land seismic energy source for seismic surveying or exploration on the earth and particularly to a pivoted elevator mounting for the generating assembly of such a land seismic energy source.
In seismic exploration on land, intense seismic impulses are transmitted down into the earth's surface at a desired site or grouping of sites, called the "shot point" or "shot points", and these impulses may be repeated at frequent intervals. A network of geophones is used to sense and to provide a recording of the results at various points spaced from the shot point or points at which the powerful sound impulses have been transmitted into the earth. These geophones are coupled to the earth for receiving the seismic energy which has been reflected and/or refracted by sub-surface geologic strata and various other sub-surface structures in the earth. Then the seismic energy generator equipment is raised from the surface of the earth and moved to the next shot point or group of shot points, and seismic impulses are then transmitted into the earth at the new shot point(s), and so on. In this manner, information is obtained about the conditions and characteristics of the geologic formations in the regions being surveyed. Such seismic surveying can be conducted on land, gravel, rocks, marshland, mud, sand, swamps or in shallow water where the land source can be positioned down against the earth.
Such land seismic energy sources have been constructed in compact and mobile form wherein the seismic energy generator includes a tank which may be in the shape of an inverted dome provided with a displaceable diaphragm bottom to enclose therein an incompressible liquid, such as water. One or more powerful gas-releasing airguns are positioned within the tank and receive and store pressurized air or other suitable gas under high pressure from a source of pressurized gas such as the high pressure receiver storage tank of a high pressure air-compressor. A metal pan is positioned between the diaphragm and the earth so that upon a very sudden or intensely abrupt release of the high-pressure gas into the liquid the flexible diaphragm suddenly thrusts down on the metal pan to displace a portion of the earth beneath the pan and thereby produce a powerful seismic impulse transmitted down into the earth.
In reaction to this transmission of a powerful seismic impulse, the seismic energy generator is forced away from the ground and, thus, seismic energy generating assemblies are generally constructed so that the energy generator is free to move within an assembly frame in reaction to transmission of the seismic impulse. Hydraulic catch cylinders are often provided to hold the energy generator away from the ground surface for a short period of time after the impulse is generated in order to avoid spurious seismic signals which would result if the energy generator were allowed to immediately fall back to its initial position.
Various lifting arrangements have been used to raise the seismic energy generator up from an operating position on the ground to an inoperative position for transport. Generally, in the prior art the seismic energy generator assembly is pivotally suspended from a supporting frame, and this supporting frame is swung upwardly along an arc to raise the seismic energy generator assembly.
Detailed information concerning prior mobile land seismic energy sources patented by the present inventor is disclosed in U.S. Pat. Nos. 3,800,907 issued Apr. 2, 1974; 3,779,335 issued Dec. 18, 1973; and 3,310,128 issued Mar. 21, 1967. A preferred generator assembly which may be used with the mounting apparatus of this invention is disclosed in an application Ser. No. 805,522, filed June 10, 1977, by the present inventor.